Frequency band handover in dual-connectivity systems

ABSTRACT

A cellular communication network may be configured to use a Long-Term Evolution (LTE) base station and a New Radio (NR) base station to implement a Non-Standalone Architecture (NSA) configuration, in an environment in which the NR base station uses multiple frequency bands that provide respective bandwidths. During an NSA connection with a mobile device, LTE signal strength is used as an indicator of whether the device is within the coverage area of a given NR frequency band. When the LTE signal strength indicates that the device has moved into the coverage area of a frequency band having a higher bandwidth than the currently active NR connection, the device is instructed to release and reestablish its NR connection in order to reconnect using the best available NR frequency band. LTE A1 and/or A5 event measurements may be used to evaluate signal strengths and as triggers for NR release/reestablish operations.

CROSS-REFERENCE TO RELATED APPLICATION

This patent application is a continuation of and claims priority to U.S.patent application Ser. No. 16/846,142, titled “FREQUENCY BAND HANDOVERIN DUAL-CONNECTIVITY SYSTEMS,” filed Apr. 10, 2020, which isnonprovisional of and claims priority to U.S. Provisional PatentApplication No. 62/965,242, titled “FREQUENCY BAND HANDOVER INDUAL-CONNECTIVITY SYSTEMS,” filed Jan. 24, 2020, both of which are fullyincorporated herein by reference.

BACKGROUND

Cellular communication devices use network radio access technologies tocommunicate wirelessly with geographically distributed cellular basestations. Long-Term Evolution (LTE) is an example of a widelyimplemented radio access technology that is used in 4^(th)-Generation(4G) communication systems. New Radio (NR) is a newer radio accesstechnology that is used in 5^(th)-Generation (5G) communication systems.Standards for LTE and NR radio access technologies have been developedby the 3rd Generation Partnership Project (3GPP) for use by wirelesscommunication carriers.

A communication protocol defined by the 3GPP, referred to asNon-Standalone Architecture (NSA), specifies the simultaneous use of LTEand NR for communications between a mobile device and a communicationnetwork. Specifically, NSA uses dual connectivity, in which the mobiledevice uses both LTE and NR communication links for transmissions to andfrom corresponding 4G and 5G base stations. An LTE link is used forcontrol-plane messaging and for user-plane communications. An NR link isused for additional user-plane bandwidth.

When using NSA, a 4G LTE base station (referred to as a Master eNodeB orMeNB) is associated with a 5G NR base station (referred to as aSecondary gNodeB or SgNB). In an NSA system, both the LTE base stationand the NR base station support a 4G core network. However, controlcommunications are between the 4G core network and the LTE base station,and the LTE base station is configured to communicate with and tocontrol the NR base station.

In an NSA system, a mobile device initially connects to an LTE basestation. When in a connected state, the LTE base station instructs thedevice to determine whether it is receiving a signal of sufficientstrength from a specified NR base station. If the device finds asufficiently strong signal from the NR base station, the LTE basestation communicates with the mobile device and the NR base station tosupply information needed to establish an NR connection between themobile device and the NR base station. After this connection isestablished, the LTE base station forwards downstream user data to theNR base station for transmission to the mobile device. In certainsituations, downstream user data may be transmitted over one or both ofthe LTE connection and the NR connection. Similarly, the mobile devicetransmits upstream user data to the NR base station using the NRconnection. In certain situations, upstream user data may be transmittedover one or both LTE and NR connections.

There are several proposed configurations for NSA dual connectivity, andcommunications between the components may be implemented in various waysin other configurations.

More and more frequency bands are being added for use with NR radioaccess technologies. Examples include bands referred to as mmW(millimeter wave), N41, N2, N66, N25, N71, etc., with more bands plannedfor the future. These various NR frequency bands support differentbandwidths. For example, mmW normally has a relatively wide bandwidthsuch as 100 MHz, 200 MHz, or 400 MHz, while N41 might have bandwidthssuch as 20 MHz, 40 MHz, 60 MHz, 80 MHz, or 100 MHz. Mid bands and lowbands FDD such as n2, n66, n71, etc., may have even lower bandwidthssuch as 5 MHz, 10 MHz, 15 MHz, or 20 MHz. Higher bandwidths allowimprovements in user throughput and user experience.

BRIEF DESCRIPTION OF THE DRAWINGS

The detailed description is described with reference to the accompanyingfigures. In the figures, the left-most digit(s) of a reference numberidentifies the figure in which the reference number first appears. Theuse of the same reference numbers in different figures indicates similaror identical components or features.

FIG. 1 is a block diagram showing relevant components of a communicationnetwork that supports Non-Standalone Architecture (NSA) dualconnectivity based on 4^(th)-Generation (4G) and 5^(th)-Generation (5G)radio access technologies.

FIG. 2 is a diagram illustrating an example of different geographiccoverage areas corresponding to different frequency bandwidths of acellular communication system.

FIG. 3 is a flow diagram illustrating an example method that may beperformed to implement 5G New Radio (NR) handovers during NSAconnections.

FIG. 4 is a block diagram of an example computing device that may beused to implement various functionality described herein.

FIG. 5 is a block diagram of an example mobile communication device thatmay be used in conjunction with the techniques described herein.

DETAILED DESCRIPTION

Described herein are techniques for triggering handovers to preferredfrequency bands in a cellular network of a wireless communicationprovider that has geographic areas of 4^(th)-Generation (4G) and5^(th)-Generation (5G) signal coverage. For example, the describedtechniques may be useful when a wireless communication device is in anarea that uses 4G and 5G radio access technologies to implementnon-standalone architecture (NSA) dual connectivity. In particular, thedescribed techniques may be used to increase the likelihood that 5G NewRadio (NR) components of a communication device are using preferredfrequency bands that allow higher data bandwidths.

When using NSA, a dual connectivity data session between a cellularcommunication device and a communication network is implemented by aprimary 4G Long-Term Evolution (LTE) data connection and a secondary 5GNR data connection. Initially, the device connects to an LTE basestation. The LTE base station is configured to communicate with anassociated NR base station in order to establish a secondary dataconnection between the device and the NR base station, using NR radioaccess technology. The primary and secondary data connections are thenused concurrently for communicating with the cellular communicationdevice.

4G and 5G cellular communication networks may utilize a number ofdifferent frequency bands. A cellular communication device will ingeneral enjoy better throughput when using higher-frequency bands, whichtypically allow higher bandwidths. However, these higher-frequency bandstend to have smaller coverage areas than lower-frequency bands.Accordingly, it may be desirable to change from one frequency band toanother as the device moves about. When a device is very near abroadcast tower, it may be desirable to use a higher-frequency band withrelatively high data bandwidths. At further distances from the tower, itmay be desirable to use lower-frequency bands that have greater coveragerange.

Unfortunately, current vendor implementations of communication device NRfunctionality do not support NR inter-frequency signal strengthmeasurements that could, if available, be used to initiate these typesof NR handovers based on NR signal strengths. That is, during connectedmode the device NR components are not configured to detect and handoverto better (i.e., higher bandwidth) NR frequency bands as those bandsbecome available. Because of this, a moving device is not assured ofusing the best NR frequency band, particularly in situations in whichthe communication device is moving toward an NR-equipped cell tower intocoverage areas of frequency bands having higher bandwidths. For example,suppose that a device establishes an NSA connection using an NR link inthe N71 band, which has a relatively large coverage area. During use,the device may move toward the cell tower and into the relativelysmaller coverage areas of higher-bandwidth frequency bands, such as themmW, n41, and n66 frequency bands. Suppose, for example, that the devicemoves toward the cellular tower and into an area in which the mmW bandis available for NR connections. In this situation, there is nomechanism for the system to detect that a more preferable NR frequencyband has become available to the device. Accordingly, the device's NRlink remains in the N71 band until released due to an event such asinactivity, even though better throughput could be achieved by handingover to a higher frequency band such as mmW.

In accordance with embodiments described herein, existing LTEinter-frequency measurement features are used to trigger reestablishmentof the NR leg of an NSA connection, thereby allowing reselection of andhandover to an NR frequency band based on current signal conditions. Insome cases, this results in a selection of a frequency band that affordshigher data throughput than the band that had previously been used forthe NR leg of the NSA connection.

In some embodiments, the currently active LTE signal is measured andused to determine whether the device might be within the coverage areaof a particular NR frequency band that has better bandwidth than thecurrently active NR frequency band. More specifically, the currentlyactive LTE signal is compared to a predetermined threshold to determinewhether the device is near enough the cellular tower so as to likely bewithin the coverage area of a given NR frequency band. Multiplethresholds may be specified, corresponding to the coverage areas ofrespective NR frequency bands, to detect movement of the device intothese coverage areas.

In some embodiments, LTE signals other than the currently active LTEsignal are measured and the measurements are used to determine whetherthe device is within the coverage area of a particular NR frequencyband. To determine whether the device is within the coverage area of aparticular NR frequency band, for example, the device measures thestrength of an LTE reference signal that is in an LTE frequency bandcoinciding with the particular NR frequency band. The measured LTEsignal strength is compared to a signal strength threshold to predictwhether the corresponding NR signal strength in the particular NRfrequency band is sufficient to support NR communications.

The LTE measurements are performed using measurement reportingfunctionality that is supported by LTE devices. More specifically, LTEcomponents of the device periodically measure signal strengths ofspecified LTE signals and generate signal event notifications inresponse to various events relating to the signal strengths. Forexample, the device may generate an LTE “A1” event when the signalstrength of the currently serving cell is greater than a configurablethreshold. Similarly, the device may generate what is referred to as an“A5” event when the signal strength of the currently serving LTE cell isless than a first configurable threshold and the signal strengthavailable from a different frequency band cell is greater than a secondconfigurable threshold. When generated, notifications of A1 or A5 eventssuch as this are sent to the LTE network, and the LTE network mayrespond as appropriate. For example, the LTE network may instruct thedevice to switch to a different cell that has a better measured signalstrength than the current cell.

In accordance with certain embodiments described herein, LTE A5measurements are made by a cellular communication device during anactive NSA connection that has been established using a first LTEfrequency band and a first NR frequency band. Specifically, A5measurements are configured to measure signal strength of an LTE signalin a second LTE frequency band, other than the currently active LTEfrequency band, so that an LTE A5 event is generated when the signalstrength in this second LTE frequency band is greater than apredetermined threshold. The second LTE frequency band in this scenariois selected as one that corresponds in frequency to an NR frequency bandhaving a higher bandwidth than the currently active NR frequency band.As an example, assume that the currently active NR frequency band is theN71 frequency band. In this case, the second LTE frequency band may bethe B41 frequency band and the higher-bandwidth NR frequency band may bethe N41 frequency band, which has a higher bandwidth than the currentlyactive NR frequency band N71.

In response to receiving the LTE A5 event, the system instructs thecommunication device to release and reestablish its NSA NR connection,with preset NR frequency priority, one example as while higher thefrequency band is, the higher predefined priority is. This allows thecommunication device, while reconnecting, to select the currentlyavailable NR frequency band having the highest bandwidth, which in thegiven example is likely to be the N41 frequency band. Using thistechnique, the communication device is able to switch tohigher-bandwidth NR frequency bands despite the unavailability of NRinter-frequency measurements and alerts.

Additionally, or alternatively, A1 events may be used to trigger ahandover to an NR frequency band having higher signal strength than theNR frequency band currently being used. Using this technique, A1measurements may be configured to measure signal strength of thecurrently active LTE signal as an indirect indicator of the strength ofa signal in a second NR frequency band, and to generate an A1 event whenthe signal strength of the current LTE signal exceeds a predeterminedthreshold. The threshold is set to an LTE signal strength value that isgreat enough to indicate that the communication device is within anestimated proximity of the cellular tower and therefore likely to bewithin the coverage area of the higher-bandwidth NR frequency band. Thistechnique relies on the assumption that the LTE signal strengthincreases as the communication device moves nearer the cellular tower.Different LTE signal strength thresholds may be used to detect coverageof different NR frequency bands.

These techniques allow an NSA connection to dynamically switch to NRfrequency bands having higher frequencies with higher bandwidths withhigher priority setting as the communication device moves toward acellular tower that supports both LTE and NR communications. This isaccomplished without NR inter-frequency measurements. The describedtechniques improve user experience by providing the highest availabledata transfer speeds.

Although the techniques are described in the context of 4G and 5Gnetworks, the techniques described herein may also be used withdifferent network types, standards, and technologies. That is, thetechniques may be used more generally for first and second wirelesscommunication networks, where a 4G network is an example of the firstwireless communication network and a 5G network is an example of thesecond wireless communication network.

FIG. 1 illustrates relevant high-level components of a cellularcommunication system 100 such as might be implemented by a cellularcommunications provider. The components shown in FIG. 1 may be used toimplement dual connectivity, for use in a Non-Standalone Architecture(NSA) configuration. When using NSA, a communication device uses both aLong-Term Evolution (LTE) carrier and a New Radio (NR) carrier foruplink and downlink transmissions to and from respective LTE and NR basestations. The LTE carrier is used for control-plane messaging and foruser-plane communications. The NR carrier is used for additionaluser-plane bandwidth.

For purposes of discussion, a 4^(th)-Generation (4G) or LTE component isa component that performs according to 4G or LTE communicationsstandards. A 4G or LTE signal or communication is a signal orcommunication that accords with 4G or LTE communications standards. A5^(th)-Generation (5G) or NR component is a component that performsaccording to 5G or NR communications standards. A 5G or NR signal orcommunication is a signal or communication that accords with 5G or NRcommunications standards.

The communication system 100 has a 4G network core 102. Thecommunication system 100 also has multiple cellular sites 104, only oneof which is shown in FIG. 1 for purposes of discussion. Although notshown, some networks may include a 5G network core.

The illustrated cellular site 104 has collocated 4G and 5G cellularaccess points, and therefore supports both 4G and 5G communications. The4G access point is implemented as an LTE base station 106, also referredto as an eNodeB, a master eNodeB, or a master base station. The 4Gaccess point is associated with a 5G access point, which is implementedas an NR base station 108. The NR base station 108 may also be referredto as a gNodeB, a secondary gNodeB, or a secondary base station. The 4Gnetwork core 102 communicates with the LTE base station 106 and the NRbase station 108. When using NSA, radio communications are controlled bythe LTE master base station. Other communication paths may be used inother embodiments.

FIG. 1 shows a single cellular communication device 110, which is one ofmany such devices that are configured for use with the communicationsystem 100. In the described embodiment, the communication device 110supports both 4G LTE and 5G NR networks and communications. Accordingly,the communication device 110 has an LTE radio 112 that communicateswirelessly with the LTE base station 106 of the cellular site 104 and anNR radio 114 that communicates wirelessly with the NR base station 108of the cellular site 104.

The communication device 110 may comprise any of various types ofwireless cellular communication devices that are capable of wirelessdata and/or voice communications, including smartphones and other mobiledevices, “Internet-of-Things” (IoT) devices, smarthome devices,computers, wearable devices, entertainment devices, industrial controlequipment, etc. In some environments, the communication device 110 maybe referred to as a User Equipment (UE) or Mobile Station (MS).

The LTE base station 106 and the NR base station 108 in the examplesdescribed below are associated with each other by being collocated at asingle cellular site. Although only a single pair of LTE and NR basestations is shown in FIG. 1 , the system 100 may include multiplecellular sites.

The communication device 110 may communicate through either or both ofthe LTE base station 106 and the NR base station 108. In some cases orembodiments, the communication device 110 may support dual connectivitycommunications, in which a single communication session concurrentlyuses both a 4G connection and a 5G connection. More specifically, thecommunication device 110 may operate using what is referred to as aNon-Standalone Architecture (NSA), using 5G NR radio technologies toaugment 4G LTE communication capabilities. When using NSA, thecommunication device 110 might use both an LTE carrier 116 and an NRcarrier 118 for downlink data reception and uplink data transmissions.The LTE carrier 116 is used for control-plane messaging and foruser-plane communications. The NR carrier 118 is used for additionaluser-plane bandwidth. The NR carrier 118 is illustrated as a dashed lineto indicate its secondary nature relative to the LTE carrier 116. Thefollowing discussion will assume that the communication device 110 is inconnected mode and using NSA.

The LTE and NR carriers 116 and 118 are implemented using signals havingfrequencies that are in respective frequency bands. The LTE frequencyband used by the LTE carrier 116 at any given time will be referred toas the active LTE frequency band. The NR frequency band used by the NRcarrier 118 at any given time will be referred to as the active NRfrequency band. It is assumed in the following examples that each of theLTE and NR base stations 106 and 108 supports multiple frequency bands.That is, each base station implements multiple cells, which correspondrespectively to different frequency bands.

FIG. 2 illustrates example coverage areas of different frequency bandsthat may be used by the LTE and NR base stations 106 and 108. Coverageareas are represented in FIG. 2 as circles, although in practice thecoverage areas might be shaped differently. The NR base station 108 inthis example supports NR bands N71, N41, and mmW, in order of increasingsignal frequency. Coverage areas of these bands are illustrated asdashed circles. The mmW band has a coverage area 202. The N41 band has alarger coverage area 204. The N71 band has an even larger coverage area208.

The different NR bands have different bandwidths. Generally,higher-frequency and higher-bandwidth bands have smaller coverage areaswhile lower-frequency and lower-bandwidth bands have larger coverageareas. In this example, the mmW band has the highest bandwidth and thesmallest coverage area. The N71 band has the largest coverage area andpotentially the lowest bandwidth due to the scarcity of low-bandresources.

As used herein, the bandwidth of a frequency band is the highest datatransfer rate that is available to a device when using a communicationsignal in that frequency band. A carrier or connection is said to use afrequency band when the carrier or connection is based on a radio signalhaving a frequency within that frequency band. The frequency band thatis being used for an active connection is referred to as the activefrequency band.

The LTE base station 106 may also support multiple frequency bands, someof which may overlap or otherwise correspond to the frequency bands ofthe NR base station 108. For example, the LTE base station 106 maysupport the B41 frequency band, which may cover the same frequency rangeand has roughly the same coverage area 204 as the N41 frequency band. Inexample of FIG. 1 , the LTE base station 106 also supports the B66 band,which is assumed in following examples to be used for LTE anchorconnections. That is, NSA connections are set up to use the B66 band forLTE communications. The B66 band has a coverage area 210.

FIG. 2 illustrates a scenario in which a wireless communication device,whose position is represented in FIG. 2 as a series of small numberedcircles, is moving toward the first and second collocated base stations106 and 108. An NSA connection is initially set up at position 1. It isassumed for purposes of description that this initial connection usesthe B66 band for LTE communications and the N71 band for NRcommunications. As the communication device moves inward toward the basestations 106 and 108, to position “2”, it may be desirable for the NRconnection to switch from the N71 band to the N41 band in order to enjoythe higher bandwidth of the N41 band. Similarly, moving inward toposition 3 should result in the NR connection switching to the mmW band.

In some embodiments, LTE A1 event measurements may be performed by thecommunication device 110 to estimate when the communication device 110is within any given NR coverage area. The A1 event measurement can beconfigured to generate a notification when the signal strength of thecurrently active LTE connection exceeds a given threshold, indicatingthat the communication device 110 is nearing the LTE and NR basestations 106 and 108. For example, A1 measurements may be used with athreshold value equal to the anticipated LTE signal strength at thepoint where the communication device 110 is at a distance from the LTEbase station 106 that is within the N41 coverage area 204. At anothertime, the A1 threshold may be set to a value equal to the anticipatedLTE signal strength when the communication device 110 is within the mmWcoverage area 202.

More specifically, when the communication device 110 is at position 1,using the N71 band for the NR connection, the A1 threshold is set to anLTE signal strength value corresponding to the next-higher NR frequencyband, which in this case is the N41 band. When the communication device110 is at position 2, using the N41 band for the NR connection, the A1threshold is set to an LTE signal strength value corresponding to thenext-higher NR frequency band, which in this case is the mmW frequencyband.

In response to an A1 event, the NR base station 108 and/or device 110are instructed to release and then reestablish the active NR connection.When reestablishing the NR connection, the communication device 110performs various NR signal measurements to determine the best (i.e.,highest bandwidth) available NR frequency band. When the communicationdevice is at position 2, N41 is the best available NR frequency band.When the communication device 110 is at position 3, the mmW band is thebest available NR frequency band. Selection of the best NR frequencyband can be achieved by setting different priorities for different NRfrequency bands. For example, higher frequency bands may be assignedhigher priority settings.

In some embodiments, LTE A5 event measurements, rather than A1 eventmeasurements, may be used to estimate when the communication device iswithin any of the NR coverage areas. In LTE systems, an LTE A5 event isgenerated when the signal strength of the currently active LTE signal isless than a first A5 threshold and the strength of a different LTEsignal is greater than a second A5 threshold. By setting the first A5threshold to a high, unobtainable value, the A5 event can be configuredto provide a notification whenever the signal strength of the differentLTE signal is greater than the second A5 threshold.

In described embodiments, the LTE A5 event is configured to be based onthe strength of a reference signal in a referenced LTE frequency bandthat corresponds in frequency to the NR frequency band that has the nexthigher frequency and bandwidth in relation to the currently active NRfrequency band. For purposes of this measurement, the first A5 thresholdis set to a very high value, and the second threshold is set to a valuecorresponding to the signal strength needed to support a dataconnection. When configured in this manner, the LTE A5 event isgenerated when the reference signal of the referenced LTE frequency bandexceeds the second A5 threshold. The A5 event is then interpreted asindicating that the NR frequency band corresponding to the referencedLTE band is likely available for use.

In a described embodiment, LTE A1 and/or A5 events, configured in thismanner, are used to trigger NR components of the NR base station 108 anddevice 110 to release the current NR connection and to establish a newNR connection. Various types of selection criteria may be used forselecting an NR frequency band when reestablishing the NR connection. Insome cases, NR frequency bands are scanned in a prioritized manner sothat higher-bandwidth bands are evaluated first. More specifically, thecellular network may first instruct the device 110 to evaluate signalstrength of a reference signal in a first frequency band having arelatively high bandwidth, and to establish an NR connection using thisfrequency band if the signal strength in the frequency band issufficient. Otherwise, if the first frequency band is not available at asufficient signal strength, the cellular network may instruct the device110 to evaluate signal strength of a reference signal in a second NRfrequency band having a relatively lower bandwidth, and to establish anNR connection using the second NR frequency band if a signal ofsufficient strength is found in that frequency band. This process may berepeated for frequency bands having successively decreasing bandwidthsuntil a qualifying (i.e., a signal of sufficient strength) NR frequencyband is identified.

The described techniques provide a mechanism for handing over between NRfrequency bands in response to changing signal conditions. Inparticular, an inter-frequency NR change is triggered in response tochanging LTE signal conditions such as indicated by LTE A5 events, LTEA1 events, and/or other detected LTE inter-frequency events. This isparticularly useful as a communication device moves into successivelysmaller coverage areas of respective higher-frequency NR frequencybands, allowing the communication device to take advantage of the higherthroughputs afforded by these frequency bands.

FIG. 3 illustrates an example method 300 that may be performed to set upand maintain a data communication session with the cellularcommunication device 110 when using dual connectivity, such as whenoperating in an NSA mode of a hybrid 4G/5G communication network. Theexample method 300 will be described in the context of FIG. 1 , althoughthe method is also applicable in other environments.

An action 302 comprises establishing a primary data connection, using afirst radio access technology such as LTE, between the cellularcommunication device 110 and the LTE base station 106. The LTE dataconnection 116 of FIG. 1 is an example of such a primary dataconnection. The LTE data connection 116 may be established by the LTEbase station 106 in accordance with 3GPP 4G LTE specifications, in anappropriate LTE frequency band that will be referred to herein as theLTE anchor frequency band. For example, the frequency band B66 may beused as the anchor frequency band. The LTE frequency band being used bythe device 110 for the LTE data connection 116 will also be referred toas the active LTE frequency band.

An action 304 comprises establishing a secondary data connection, usinga second radio access technology such as 5G NR, between the cellularcommunication device and the NR base station 108. The NR data connection118 of FIG. 1 is an example of such a second data connection. The NRdata connection 118 serves as a secondary data connection when using NSAdual connectivity. NR connections such as this are implemented inaccordance with 3GPP 5G NR and NSA specifications, in an appropriate NRfrequency band. The action 304 may include configuring the NR basestation 108 to transmit and receive data, using the NR data connection118, as part of an NSA data session with the device 110. The NRfrequency band being used by the device 110 for the NR data connection118 will be referred to herein as the active NR frequency band.

When establishing the NR data connection 118, the device 110 may scan NRreference signals in multiple NR frequency bands in order to identifythe best available NR frequency band, such as a frequency band thatprovides the greatest bandwidth among the NR frequency bands whosereference signals have acceptable signal strengths. For example, thedevice 110 may first determine whether a reference signal in the mmWband has an acceptable signal strength and, if so, may establish the NRdata connection 118 using that frequency band. Otherwise, the device 110may then check the frequency band having the next lower bandwidth, whichin the example of FIG. 2 would be the N41 band. The device 110successively scans reference signals of the frequency bands in order ofdecreasing bandwidth until finding a frequency band having a referencesignal with an acceptable signal strength. When the device 110 finds afrequency band whose reference signal has an acceptable signal strength,the NR connection 118 is established using a carrier in this frequencyband and the device 110 does not scan any lower-bandwidth frequencybands.

An action 306 relates to a countdown timer that may be used in someembodiments to prevent repeated unsuccessful attempts of NR connectionhandovers, and which will be discussed in more detail at a later pointin this description. Initially, it can be assumed that there is noactive timer and that the action 308 is performed of setting an LTEsignal strength threshold to a value T. As will be described in moredetail below, the LTE signal strength threshold is set to a value thatcorresponds to an expected minimum LTE signal strength when the device110 enters and/or is within the coverage area of a given NR frequencyband.

An action 310 comprises measuring the strength of an LTE referencesignal. For example, the action 310 may comprise measuring the referencesignal received power (RSRP) of an LTE reference signal in either theactive LTE frequency band or another LTE frequency band, as will bedescribed below.

An action 312 comprises determining whether the measured LTE signalstrength exceeds the LTE signal strength threshold. If the measured LTEsignal strength exceeds or otherwise satisfies the LTE signal strengththreshold, an action 314 is performed of sending a signal eventnotification to the LTE base station 106.

The actions 310, 312, and 314 may in some embodiments be implemented byLTE A1 and/or A5 measurements performed by the device 110. A1 and A5measurements, grouped in FIG. 3 by a dashed box and referenced by thenumeral 316, are used in LTE systems for facilitating handovers betweenLTE base stations. The device 110 can be configured by the LTE basestation 106 to perform A1 and/or A5 measurements in accordance withspecified parameters. Specifically, the LTE base station 106 specifiesthe signal strength threshold(s) used by the A1/A5 measurements and inthe case of A5 measurements can also specify the LTE frequency band inwhich measurements will be performed. The purpose of these measurementsin this context is to estimate the current signal strength of a signalin a particular NR frequency band, and to generate an event notificationto the LTE base station 106 when the estimated NR signal strength issufficient to support an NR data connection.

In some embodiments, A1 measurements are used to evaluate likely signalstrength of different NR frequency bands based on a signal strength thatis observed in the active LTE frequency band. More specifically, adifferent LTE signal strength threshold (i.e., the threshold T) may bespecified for each of multiple NR frequency bands. When the measuredsignal strength of the current LTE connection 116 exceeds the thresholdthat has been specified for a particular NR frequency band, the A1 eventis generated and that NR frequency band is assumed to be of a sufficientsignal strength to support an NR connection.

At any given time, the signal strength threshold T used for A1measurements may be selected based on which of the NR frequency bands iscurrently active (i.e., the NR frequency band currently being used forthe NSA connection). For a particular active NR frequency band, an A1LTE signal strength threshold corresponding to the NR frequency bandhaving the next highest bandwidth is selected. As an example, supposethat the device 110 is in position 2 of FIG. 2 , and is using the N41frequency band. In this situation, the A1 LTE signal strength thresholdis set to a value that is likely to be present when the device 110 movesgeographically into the mmW frequency band, such as to position 3 ofFIG. 2 . This results in an A1 event notification being produced eachtime the device 110 moves into the coverage area of an NR band having ahigher bandwidth than the currently active NR frequency band. The actualthreshold values for the different NR frequency bands may be determinedby experimentation and observation of existing installations.

In some embodiments, A5 measurements may be used to evaluate likelysignal strength of different NR frequency bands based on LTE signalstrengths of reference signals in corresponding LTE frequency bands,including the active LTE frequency band and other LTE frequency bands.A5 measurements are based on a first A5 threshold and a second A5threshold. The A5 event notification is generated when (a) the signalstrength of the currently active LTE connection is less than the firstA5 threshold and the signal strength observed from a specified“neighboring” cell is greater than the second A5 threshold. Inaccordance with the techniques described herein, the first A5 thresholdis set to a value that is higher than any expected LTE signal strengthso that the first threshold is always satisfied. That is, the signalstrength of the currently active LTE connection will always be less thanthe first A5 threshold. As a result of this, the A5 notification will begenerated whenever a reference signal of the “neighboring” cell isgreater than the second A5 threshold, without regard for the signalstrength of the active LTE frequency band.

In the described environment, the different LTE frequency bandssupported by the LTE base station 106 are considered as being providedby different cells, and the A5 measurement can be configured to measuresignal strength in any of these LTE frequency bands. In accordance withthe techniques described herein, the LTE frequency band to be evaluatedagainst the second A5 threshold is selected based on the currentlyactive NR frequency band. For any particular active NR frequency band,the NR frequency band having the next-highest bandwidth is identified.The LTE frequency band corresponding to this next-higher NR frequencyband is then specified as the LTE frequency band to which the second A5threshold is to be compared. The LTE frequency band is selected suchthat it and the next-highest NR frequency band span at least a commonfrequency range. In some cases, the selected LTE frequency band may spanthe same frequency range as the next-higher NR frequency band.

As an example, suppose that the device 110 is in position 1 of FIG. 2and is using the N71 frequency band for an NR connection. In thissituation, the N41 band is the next-higher bandwidth frequency band. TheB41 band is the corresponding LTE frequency band and is specified as thesubject of the LTE A5 measurement. The second A5 threshold is set to anLTE signal strength value which, if exceeded, indicates that the signalstrength in the N41 frequency band is likely sufficient to support an NRconnection. Accordingly, as the device 110 moves into the N41 coveragearea 210, an A5 event is generated based on the strength of an LTEreference signal in the LTE B41 frequency band. Using this technique, anA5 event is generated each time the device 110 moves into the coveragearea of an NR band having a higher bandwidth than the currently activeNR frequency band.

An action 318, performed by the LTE base station 106, comprisesreceiving an LTE A1 or LTE A5 signal event notification from the device110, which has been generated by the device 110 as described above.

In response to receiving the A1 or A5 signal event notification, anaction 320 is performed of first releasing the current NR connection 118and then reestablishing the NR connection 118. For purposes ofdiscussion, the combination of these actions will be described as arelease/reestablish operation 320.

The release/reestablish operation 320 includes an action of identifyinga new NR frequency band that is (a) currently available for use by thedevice 110 and (b) has a greater bandwidth than the original, previouslyactive NR frequency band. This can be achieved by initiating a new B1measurement procedure, in which priority is given to higher-bandwidth NRfrequency bands so that the reestablished NR connection uses thehighest-bandwidth frequency band that is currently available to thedevice 110. In some embodiments, this may be accomplished by instructingthe cellular communication device to search, using B1 measurementtechniques, for an NR signal in a sequence of NR frequency bands havingsuccessively decreasing bandwidths. More specifically, the device 110performs signal measurements of reference signals in different NRfrequency bands, in a prioritized sequence of NR frequency bands inwhich higher-frequency and higher-bandwidth frequency bands areprioritized over lower-frequency and lower-bandwidth frequency bands.The device 110 reestablishes the NR connection using the first NRfrequency band in the sequence that has a corresponding NR referencesignal of an acceptable signal strength.

In some embodiments, an action 322 may be performed to reduce frequentNR connection release/reestablish operations, which might otherwiseoccur when the release/reestablish operation 320 does not result in achanged NR frequency band. For example, in some cases the action 320 maycomprise releasing an NR connection that has been using a particularfrequency band, and then reconnecting using that same NR frequency band.This might happen particularly when using A1 measurements because the A1thresholds are only indirectly related to NR signal strengths in thevarious NR frequency bands.

The action 322 comprises determining whether the release/reestablishoperation 320 resulted in a change in the active NR frequency band. Ifthere was no change, and the reestablished NR connection uses the samefrequency band as the released NR connection, an action 324 is performedof activating a countdown timer. If there has been a change in the NRfrequency band, an action 326 is performed of inactivating the countdowntimer. The countdown timer is a logical construct or flag that whenactivated remains active or “true” for a configurable time or untilotherwise inactivated. The countdown timer is initiated when therelease/reestablish operation 320 results in selection of the samefrequency band as was being used when the secondary connection wasreleased. As will be discussed, the countdown timer prevents anysubsequent releasing of the secondary data connection for at least apredetermined time period to prevent repeated unsuccessful attempts tomove to a higher bandwidth frequency band.

Returning to the action 306, the signal strength threshold is set to adifferent value when the countdown timer is active. If the countdowntimer is inactive, subsequent actions starting at the action 308 areperformed as already described, with the signal strength thresholdhaving a value T, which may vary depending on the currently active NRfrequency band. If the countdown timer is active, however, the signalstrength threshold is increased by a ramp-up value D (i.e., T+D) in anaction 328, wherein D is a preselected value such as +10 dBm, forexample. The remaining actions of FIG. 3 are then performed, starting atthe action 310, using this increased signal strength threshold T+D. Thisprovides an override to the disabling effect of the countdown timer incases where there is a significant increase in signal strength of themeasured LTE frequency band.

FIG. 4 is a block diagram of an illustrative computing device 400 suchas may be used to implement various components of a core network, a basestation, and/or any servers, routers, gateways, administrativecomponents, that may be used within a communications network. One ormore computing devices 400 may be used to implement each of the basestations 106 and 108, for example. Similarly, one or more computingdevices may be used to implement components of the 4G network core 102.

In various embodiments, the computing device 400 may include at leastone processing unit 402 and system memory 404. Depending on the exactconfiguration and type of computing device, the system memory 404 may bevolatile (such as RAM), non-volatile (such as ROM, flash memory, etc.)or some combination of the two. The system memory 404 may include anoperating system 406, one or more program modules 408, and may includeprogram data 410.

The computing device 400 may also include additional data storagedevices (removable and/or non-removable) such as, for example, magneticdisks, optical disks, or tape. Such additional storage devices areillustrated in FIG. 4 as storage 412.

Non-transitory computer storage media of the computing device 400 mayinclude volatile and nonvolatile, removable and non-removable media,implemented in any method or technology for storage of information, suchas computer readable instructions, data structures, program modules, orother data. The system memory 404 and storage 412 are all examples ofcomputer-readable storage media. Non-transitory computer-readablestorage media includes, but is not limited to, RAM, ROM, EEPROM, flashmemory or other memory technology, CD-ROM, digital versatile discs (DVD)or other optical storage, magnetic cassettes, magnetic tape, magneticdisk storage or other magnetic storage devices, or any other mediumwhich can be used to store the desired information and which can beaccessed by computing device 400. Any such non-transitorycomputer-readable storage media may be part of the computing device 400.

In various embodiment, any or all of the system memory 404 and storage412 may store programming instructions which, when executed, implementsome or all of the function functionality described above.

The computing device 400 may also have input device(s) 414 such as akeyboard, a mouse, a touch-sensitive display, voice input device, etc.Output device(s) 416 such as a display, speakers, a printer, etc. mayalso be included. The computing device 400 may also containcommunication connections 418 that allow the device to communicate withother computing devices.

FIG. 5 illustrates an example cellular communication device 500 that maybe used in conjunction with the techniques described herein. Signalstrength measuring and generation of A1 and A5 signal events may beperformed by the device 500, for example. The device 500 is an exampleof the communication device 110, illustrating additional high-levelcomponents that are not shown in FIG. 1 .

The device 500 may include memory 502 and a processor 504. The memory502 may include both volatile memory and non-volatile memory. The memory502 can also be described as non-transitory computer-readable media ormachine-readable storage memory, and may include removable andnon-removable media implemented in any method or technology for storageof information, such as computer executable instructions, datastructures, program modules, or other data. Additionally, in someembodiments the memory 502 may include a SIM (subscriber identitymodule), which is a removable smart card used to identify a user of thedevice 500 to a service provider network.

The memory 502 may include, but is not limited to, RAM, ROM, EEPROM,flash memory or other memory technology, CD-ROM, digital versatile discs(DVD) or other optical storage, magnetic cassettes, magnetic tape,magnetic disk storage or other magnetic storage devices, or any othertangible, physical medium which can be used to store the desiredinformation. The memory 502 may in some cases include storage media usedto transfer or distribute instructions, applications, and/or data. Insome cases, the memory 502 may include data storage that is accessedremotely, such as network-attached storage that the device 500 accessesover some type of data communication network.

The memory 502 stores one or more sets of computer-executableinstructions (e.g., software) such as programs that embody operatinglogic for implementing and/or performing desired functionality of thedevice 500. The instructions may also reside at least partially withinthe processor 504 during execution thereof by the device 500. Generally,the instructions stored in the computer-readable storage media mayinclude various applications 506 that are executed by the processor 504,an operating system (OS) 508 that is also executed by the processor 504,and data 510.

In some embodiments, the processor(s) 504 is a central processing unit(CPU), a graphics processing unit (GPU), both CPU and GPU, or otherprocessing unit or component known in the art. Furthermore, theprocessor(s) 504 may include any number of processors and/or processingcores. The processor(s) 504 is configured to retrieve and executeinstructions from the memory 502.

The device 500 may have interfaces 512, which may comprise any sort ofinterfaces known in the art. The interfaces 512 may include any one ormore of an Ethernet interface, wireless local-area network (WLAN)interface, a near field interface, a DECT chipset, or an interface foran RJ-11 or RJ-45 port. A wireless LAN interface can include a Wi-Fiinterface or a Wi-Max interface, or a Bluetooth interface that performsthe function of transmitting and receiving wireless communicationsusing, for example, the IEEE 802.11, 802.16 and/or 802.20 standards. Thenear field interface can include a Bluetooth® interface or radiofrequency identifier (RFID) for transmitting and receiving near fieldradio communications via a near field antenna. For example, the nearfield interface may be used for functions, as is known in the art, suchas communicating directly with nearby devices that are also, forinstance, Bluetooth® or RFID enabled.

The device 500 may also have an LTE radio 514 and a 5G radio 516, whichmay be used as described above for implementing dual connectivity inconjunction with an eNodeB and a gNodeB. The radios 514 and 516 transmitand receive radio frequency communications via an antenna (not shown).

The device 500 may have a display 518, which may comprise a liquidcrystal display (LCD) or any other type of display commonly used intelemobile devices or other portable devices. For example, the display518 may be a touch-sensitive display screen, which may also act as aninput device or keypad, such as for providing a soft-key keyboard,navigation buttons, or the like.

The device 500 may have input and output devices 520. These devices mayinclude any sort of output devices known in the art, such as speakers, avibrating mechanism, or a tactile feedback mechanism. Output devices mayalso include ports for one or more peripheral devices, such asheadphones, peripheral speakers, or a peripheral display. Input devicesmay include any sort of input devices known in the art. For example, theinput devices may include a microphone, a keyboard/keypad, or atouch-sensitive display. A keyboard/keypad may be a push button numericdialing pad (such as on a typical telemobile device), a multi-keykeyboard (such as a conventional QWERTY keyboard), or one or more othertypes of keys or buttons, and may also include a joystick-likecontroller and/or designated navigation buttons, or the like.

Although features and/or methodological acts are described above, it isto be understood that the appended claims are not necessarily limited tothose features or acts. Rather, the features and acts described aboveare disclosed as example forms of implementing the claims.

What is claimed is:
 1. A method, comprising: establishing a Long-TermEvolution (LTE) data connection between a cellular communication deviceand an LTE base station using a first LTE frequency band, wherein theLTE base station is associated with a New Radio (NR) base station fordual connectivity; establishing an NR data connection between thecellular communication device and the NR base station using a first NRfrequency band, wherein the LTE data connection and the NR dataconnection are used concurrently for dual connectivity with the cellularcommunication device; receiving a signal event notification generated bythe cellular communication device, wherein the signal event notificationindicates that an LTE signal strength measured by the cellularcommunication device is greater than a threshold; in response toreceiving the signal event notification, releasing the NR dataconnection; identifying a second NR frequency band that is (a) currentlyavailable for use by the cellular communication device and (b) has agreater bandwidth than the first NR frequency band; and reestablishingthe NR data connection using the second NR frequency band in response tothe second NR frequency band having the greater bandwidth than the firstNR frequency band.
 2. The method of claim 1, wherein: the LTE signalstrength measured by the cellular communication device is of an LTEreference signal in the first LTE frequency band; and the signal eventnotification comprises an LTE A1 event notification.
 3. The method ofclaim 1, wherein: the LTE signal strength measured by the cellularcommunication device is of an LTE reference signal in a second LTEfrequency band; and the second LTE frequency band and the second NRfrequency band span at least a common frequency range; and the signalevent notification comprises an LTE A5 event notification.
 4. The methodof claim 1, wherein identifying the second NR frequency band comprisesinstructing the cellular communication device to search for an NR signalin a sequence of NR frequency bands having successively decreasingbandwidths.
 5. The method of claim 1, further comprising configuring theLTE data connection and the NR data connection to implement aNon-Standalone Architecture (NSA) of a 5th-Generation (5G) communicationnetwork.
 6. A system, comprising: one or more processors; and one ormore non-transitory computer-readable media storing computer-executableinstructions that, when executed by the one or more processors, causethe system to perform actions comprising: establishing a Long-TermEvolution (LTE) data connection between a cellular communication deviceand a first LTE base station using a LTE frequency band, wherein the LTEbase station associated with a New Radio (NR) base station for dualconnectivity; establishing an NR data connection between the cellularcommunication device and the NR base station using a first NR frequencyband, wherein the LTE data connection and the NR data connection areused concurrently for dual connectivity with the cellular communicationdevice; receiving a signal event notification indicating that an LTEsignal strength measured by the cellular communication device andassociated with a third frequency band has a signal strength that isgreater than a threshold, the third frequency band being a next highestfrequency band from the first NR frequency band; in response toreceiving the signal event notification, releasing the NR dataconnection; and reestablishing the NR data connection using a second NRfrequency band having a greater bandwidth than the first NR frequencyband.
 7. The system of claim 6, wherein the radio signal of the firstradio access technology is in the first frequency band.
 8. The system ofclaim 7, wherein the signal event notification comprises an A1 eventnotification.
 9. The system of claim 6, wherein the radio signal of thefirst radio access technology is in a fourth frequency band that atleast partially overlaps the third frequency band.
 10. The system ofclaim 9, wherein the signal event notification comprises an A5 eventnotification.
 11. The system of claim 6, the actions further comprising:determining that the third frequency band is the second frequency band;and in response to determining that the third frequency band is thesecond frequency band, preventing a subsequent releasing of thesecondary data connection for at least a predetermined time period. 12.The system of claim 6, the actions further comprising configuring theprimary data connection and the secondary data connection to implement aNon-Standalone Architecture (NSA) of a 5th-Generation (5G) communicationnetwork.